Even though the man – arrested on suspicion of being drunk and disorderly – is also sat on the floor, wearing a spit-hood and posing no apparent threat, Mettler slaps him hard.

The impact of the blow sends the man sideways, while two colleagues look on.

Matthew Mettler enters the holding pen, where the suspect has his hands and legs cuffed, and is sitting on the floor wearing a spit hood (San Joaquin Sheriff’s Office/YouTube)He approaches the suspect as two colleagues look on (San Joaquin Sheriff’s Office/YouTube)

A post on the Sheriff’s department Facebook page concedes ‘The detainee was sitting, legs and arms cuffed, and apparently posing no threat.’

‘Individuals who abuse their power and position will be tried and punished to the full extent of the law.’Defense Attorney Johnny Griffin explained to KCRA3 that there needs to be a ‘legal or lawful necessity’ for an official to touch or physically harm someone in custody.Mettler was reported by two police officers who witnessed what he did.He will appear at San Joaquin County Court on March 26 for a motion hearing, and has since been placed on administrative leave.